OBESITY, MONOGENIC NONSYNDROMIC

Obesity occurs as a result of alterations in the balance between food intake and energy expenditure. The hypothalamus plays a major role in the regulation of this energy balance. In response to signals from several endocrine hormones such as insulin, leptin, and ghrelin, neurons in the arcuate nucleus of the hypothalamus release various peptides. Orexigenic neurons produce agouti-related protein (AGRP) and neuropeptide Y (NPY), promoting food intake and reducing energy expenditure, while anorexigenic neurons produce pro-opiomelanocortin (POMC) and cocaine-and amphetamine-related transcript (CART), producing the opposite effect. These signals are then sent to downstream effector neurons which also receive inputs from other signaling systems to regulate food intake and energy expenditure.

In recent years, mutations in genes involved in leptin signal pathway have been found to cause rare monogenic obesity. The PCSK1 gene encodes for proprotein convertase-1/3 (PC1/3), a neuroendocrine convertase belonging to a family of subtilisin-like serine endoproteases that processes hormone precursors into functional products. A number of its substrates are required for proper energy balance including proinsulin, proglucagon, progastrin and POMC. Maturation of PC1/3 itself requires autocatalytic cleavage of a propeptide. Mutations in PC1/3 lead to a loss of enzymatic activity and impaired prohormone processing. PC1/3 deficiency is characterized by a neonatal onset enteropathy, early-onset obesity, hyperphagia and reactive hypoglycemia inherited in an autosomal recessive manner. Sequence analysis of the entire PCSK1 gene is available on a clinical basis at the Medical Genetics Laboratories at Baylor College of Medicine.

Reasons For Referral:

• Confirmation of clinical diagnosis
• Carrier testing of known familial mutations

Testing Methodology:

PCR amplification of the exons in the entire coding region of the PCSK1 gene will be performed on patient genomic DNA. Direct sequencing of amplification products is performed in both the forward and reverse directions using automated fluorescence dideoxy sequencing methods.

Specimen Requirements:

Blood: EDTA (purple-top) tubes: Adults: 14 cc; Child: 6 cc; Infant: 2-3 cc
Requisition form must accompany specimen. Prior to any genetic testing, we recommend genetic counseling and request that the subject, or their legal guardian, sign our consent form and submit it with the sample.

Turnaround Time:

Index: 4 weeks
Known Familial Mutation: 3 weeks

CPT Codes and Prices:

Index: 83912, 83894, 83891, 83898x15, 83904x30, 83909x30
Known Familial Mutation: 83912, 83894, 83891, 83898, 83904x2, 83909x2

Shipping Information

Forms:

 >> Gene Sequencing Requisition

References:

1. Jackson RS, Creemers JW, Ohagi S, Raffin-Sanson ML, Sanders L, Montague CT, Hutton JC, O'Rahilly S (1997). Obesity and impaired prohormone processing associated with mutations in the human prohormone convertase 1 gene. Nat. Genet. 16(3): 303-6.

Test Codes:

Index: 6855
Known Familial Mutation: 6856

Medical Genetics Laboratories
Baylor College of Medicine · Houston, TX 77030
Phone: 1-800-411-GENE · Fax: 713-798-2787
E-mail: